1. Field of the Invention
The present invention relates to multimedia broadcasts, and more particularly, to a method for canceling interference of multimedia broadcasts and a communication terminal for the same.
2. Discussion of the Related Art
A signal transmitted using Code Division Multiplexing (CDM) typically arrives at a receiver over a multipath channel. When signals are received over multipath channels, inter-channel or inter-signal interference occurs due to factors such as power difference between the channels. On the other hand, when signals are received over single-path channels, no inter-channel or inter-signal interference occurs since the channels do not affect each other. A number of interference cancellation techniques have been introduced to cancel such multipath channel interference.
Recently, multimedia broadcasts have been introduced and implemented. Multimedia broadcasts can be defined as digital broadcasts that can provide audio, video, and data services with high quality sound and images and high quality stationary and mobile reception. Digital Multimedia Broadcasts (DMBs), which have also been introduced, are divided into terrestrial and satellite DMBs depending on whether a terrestrial or satellite band is used to transmit the DMB signals.
When CDM is used to transmit a broadcast signal, the broadcast signal arrives at a broadcast terminal over a multipath channel. A transmitter transmits channels after coding and multiplexing the channels using orthogonal codes allocated to the channels. One example of orthogonal codes are Walsh codes.
Although channels have been described above as the subject of coding, multiplexing, and transmission, it is actually broadcast signals that are the subject to coding, multiplexing, and transmission. However, since expressions such as “to code channels”, “to multiplex channels”, and “to transmit channels” are commonly used, the terms “channels” and “signals” in the following description are used synonymously to describe the subject of coding, multiplexing, and transmission.
When CDM is used for broadcast signal transmission and a number of Walsh codes are used as orthogonal codes for the CDM transmission, a channel or signal that is coded using a Walsh code ‘0’ is a pilot channel over which a pilot signal is transmitted. Channels coded using the remaining Walsh codes are CDM channels over which broadcast signals are transmitted.
The pilot signal transmitted over the pilot channel includes channel information such as channel gain and phase information and also includes information required for decoding, such as interleaving type or Fast Error Correction (FEC) information. The pilot channel uses higher power than CDM channels over which broadcast signals are transmitted since the pilot channel transmits more important information than CDM channels. For example, the pilot channel uses transmission power that is 3 dB higher than CDM channels. Because the pilot channel uses higher transmission power than CDM channels, information required for decoding, such as channel information, may be more accurately estimated from the pilot channel.
However, the pilot channel may cause interference with CDM channels since the pilot channel uses higher transmission power than CDM channels. Therefore, although the information required for decoding, such as channel information, can be more accurately estimated by increasing the transmission power of the pilot channel, the high transmission power of the pilot channel reduces the reception quality of broadcast signals that are received over CDM channels.